Fireworks are constructed of powder and other materials that can readily release light and heat by oxidation reaction. Pyrotechnic compositions are highly susceptible and readily result in explosive decomposition. Fireworks have led to numerous accidents during their manufacture, storage, and display. Water as an impurity affects the decomposition properties of fireworks, and consequently influences their emission safety. This research focused on the thermal stability of multiple tubes of propellant, effect pieces, and propellant mixed with water using differential scanning calorimetry (DSC) and thermokinetic analysis. The thermokinetic method was employed to determine the apparent activation energy and predict the long-term stability of dry and humid propellants. According to the predicted results, the decomposition of dry and humid propellants was severely limited after 30 days at an isothermal condition of 80 °C. However, the DSC tests indicated that water could substantially influence the heat release, emission ability, and sensitivity of the propellant. The exothermic peak for the humid propellant was ca. 275 °C, which was lower than dry propellant of 318 °C. The water visibly diminished the heat emitted from and peak intensity of the propellant. Insufficient energy supply might result in lower emission height, and lower exothermic onset temperatures in wetted propellant could lead to faulty ignition times. Therefore, contact with water (that could lead to water infiltration) should be avoided to increase the probability of successful launching and ignition.